Is this useful?
We're restarting the server later anyway, and, assuming `reload_signal` is usually `HUP`, this will just send an additional sigterm (according to [SS docs](https://metacpan.org/module/KAZUHO/Server-Starter-0.15/start_server#signal-on-hup-SIGNAL)).

Because of this, I think we don't need `reload_signal` option for this service class, just boolean `proxy_logs` flag, and then you can send `HUP` to `ubic-guardian` if it's enabled. (Or just send it in any case, since `ubic-guardian` will ignore `HUP` if logs are not proxying.)